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Termites of the Amazon rainforest – part 3

Some termite species of the Amazon build nests at ground level – termite mounds – for instance Neocapritermes braziliensis. This species has soldiers with large yellowish heads and bright black, asymmetric, snapping mandibles; it feeds on very rotten wood in contact with soil. Interestingly, it has been shown that a crocodilian species (Paleosuchus trigonatus) that lives in rainforest streams builds its nests on N. braziliensis mounds. Mounds, in turn, produce heat and help regulating crocodilian egg temperature and development[10].

Termes spp. also build nests similar to those of N. braziliensis and also have asymmetric mandibles, although they feed mainly on less decayed wood (which is reflected in their more carton-like nest walls). Other easily detectable species include Embiratermes neotenicus, a mandibulate nasute that builds conspicuous, clayish mounds, and Rotunditermes bragantinus, a small nasute species that builds carton mounds.

Several termites seem to forage mainly at night, perhaps because it is safer from predators. For instance, during the last hours of the day, it is easy to see hordes of S. molestus harvesting dead leaves on the ground. Nonetheless, most described species were collected from the underground or from within wood with no apparent signs of habitation, which suggests extremely cryptic life habits. Hence, what has already been experienced from Amazonian termites is likely to be the tip of an iceberg only.

Surveys on termites in the Amazon

Beyond species surveys, research on Amazonian termites is still incipient. In 1994, C. Martius (the German biologist) published a synthesis of what was then known about termites in the Amazon[12]. Almost two decades latter, it remains the main reference on the subject. Estimated average biomass of termites in Amazonian forests varies widely. In his synthesis, Martius calculated it as around 20 kg/ha based on a few previous studies. Four years later, his own research, especially focusing on Syntermes spp., led him to raise this to 30 – 35 kg/ha[2]. More recently, Akinori Yamada’s research on termite roles in tropical ecosystem functioning resulted in an even higher estimate, ca. 68 kg/ha 2. Average animal biomass in the Amazon rainforest has been roughly estimated as 100 kg/ha.

Thus, these insects may represent over half the total animal matter – at least in some areas! Also highly variable are the figures for their role in decomposition: it has been calculated that termites remove about 38% of the leaf litter during the rainy season, which suggests a role in nutrient cycling even more pronounced than that of fungi[13] – although this does not account for other sources of carbon, such as dead trunks. Yamada’s research indicated that termites are responsible for mineralizing ca. 77 kg of organic carbon per hectare from a total input of 5,780 tons C/ ha/ year, which means a modest 1.3%. Nevertheless, these estimates are not representative of the entire forest, since they are all derived from a few areas close to research centers in a region of continental dimensions.

There are few regional institutions currently supporting studies on termites, such as the National Institute for Amazon Research in Northern Brazil, but these efforts are scattered. There is nothing like the well-established Termite Research Group at London’s Museum of Natural History – and there isn’t a single termite native to Britain! Most importantly, little attention has been paid to the causes underlying the observed patterns of termite distribution and diversity. Besides, although conspicuous termite nests are frequent in some areas of the region, few researchers have taken advantage of this feature to focus on their population and/or colony biology in any detail. Even worse, part of this work has been carried out solely as PhD. theses and remains unpublished.

Influences on termite spatial population

Termites, as all other known living beings, show an intrinsic tendency to multiple. Therefore, in the absence of any constraints, termite populations should grow geometrically, eventually covering the whole world! This, of course, does not happen, and several factors have been suggested to limit termite populations. Spatial variation in such factors implies variation in the size of different local populations and hence, variation in termite abundance. Termites are territorial, which suggests that they may compete for space both intra and interspecifically. Although food does not generally seem to limit termite occurrence in rainforests, both dead wood and soil organic matter are not homogeneously distributed in space, and this may cause variation in termite abundance.

Most termites are small, fragile and easily affected by excessive light and high thermal amplitude. In the forest, natural gaps form after old trees fall, and this may prevent local maintenance of some species (or perhaps facilitate that of some others). Since many termite species feed on soil and several build structures from soil, soil composition in likely to influence termite establishment. Finally, as social insects, termites live in aggregations easily spotted by predators: termite colonies are sessile, renewable sources of animal nutrients. The American biologist Edward O. Wilson wrote, “The worst enemy of a social insect is another social insect”. Indeed, ants are one of the main natural threats to termites; some ants are strictly termitophagous, by virtually any ant will prey upon any termite if given the chance.

The effects of most of these factors on wild termite populations are still waiting for proper investigation. Studying one or another in isolation won’t help, because all these things may be working at the same time, at different levels (colony/population), and the truly relevant question then is how each species responds to them. One important thing to note is that environmental effects may be more or less relevant in explaining termite distributional patterns depending on the considered scale. For instance, climate may be very important in governing broad differences in species composition among different parts of the Amazon basin, but biotic interactions such as competition and predation may be more important in limiting termite populations at local scale.

We need the termites too

The study of Amazonian termites is sill waiting to be broadened so that the available, worldwide knowledge on the subject can benefit from the rich termite diversity found in this remarkable rainforest. Such information would also help in assessing termite ecological roles more accurately, such as their contribution to nutrient cycling, the global methane budget and ecosystem engineering (i.e. the physical modification of the environment). This leads us right back to where we started from: should we really care about studying termites anyway?

Albert Einstein allegedly said once “if the bee disappears off the surface of the globe, then man would only have four years of life left”. Bees are major pollinators; hence no bees, no crops, no humans. Similarly, termites are like nature’s garbage men in the tropics, recycling what tastes like waste for most others and organizing whole ecosystems in this way – “the little things that run the world”, as Edward O. Wilson put it. Understanding the termite way will allow us to predict it and, eventually, control it. The relevance of this in the context of current climate change and biodiversity crisis driven by human civilization should be obvious – that is, if we still care about our own future on Earth, of course. We need termites, and bees, and most other invertebrates. They don’t need us!